Surface treatment method

ABSTRACT

A surface treatment method is disclosed. The surface treatment method forms a matte nickel plating layer on a substrate, followed by the brushed finishing and degreasing processes. The degreasing processes includes ultrasonic degreasing and electrolytic degreasing. Next, an acid activation is performed before the formation of a non-leveling nickel plating layer. Finally, a chromium plating layer and a PVD chromium film are sequentially formed. The present invention provides a high quality metal appearance and enhanced corrosion resistance with reduced cost.

BACKGROUND OF THE INVENTION Technical Field

The present invention is related to a surface finishing method, and,more particularly, to a surface treatment method that can provide acorrosion-resistant surface with high quality metal appearance.

Description of Related Art

Chromium plating is a process that has been utilized for many years toprovide a decorative chromium finish on a metal surface of a metal orplastic base material. Chromium plating may be applied to a variety ofproducts, such as the bathroom fittings, consumer electronics,automobiles, etc., where the appearance of metal finishes is asignificant concern. While chromium plating of metal surfaces has beenutilized for many years, it is expensive and has corrosion issues.

Over time, alternatives to these metal chromium plating processes havebeen developed. Some of these developments were made in response toconcerns over the use and disposal of hexavalent chromium and heavymetals typically used in the plating process. Additionally, regulationssurrounding the use of hexavalent chromium have become more restrictive,causing efforts aimed at developing alternative technologies tocorrespondingly increase. A number of commercial chemistries usingtrivalent chromium have been offered as replacements for hexavalentchromium in the plating process to address these concerns. Processesusing these chemistries, however, provide decreased corrosion protectionand are significantly more expensive.

It would therefore be desirable for economic and environmental reasonsto develop an alternative technique or process capable of providingcorrosion resistance that can be utilized in industries where thesurfaces would be subjected to environmental and mechanical stresseswith cost savings.

BRIEF SUMMARY OF THE INVENTION

In view of the above, the purpose of the present invention is to providea surface treatment method which can provide a corrosion-resistantsurface with high quality metal appearance and reduce cost.

The present invention provides a surface treatment method including thefollowing steps: forming a matte nickel plating layer on a substrate;performing a brushed finishing to the matte nickel plating layer to forma brushed surface on the substrate; performing an ultrasonic degreasingto the brushed surface to form an ultrasonically degreased surface;performing an electrolytic degreasing to the ultrasonically degreasedsurface to form an electrolytically degreased surface; performing anacid activation to the electrolytically degreased surface to form anacid-activated surface; forming a non-leveling nickel plating layer onthe acid-activated surface; forming a chromium plating layer on thenon-leveling nickel plating layer; and forming a chromium film on thechromium plating layer by physical vapor deposition.

The advantage of the present invention is that the surface treatmentmethod can provide high quality metal appearance comparable with thatprovided by trivalent chromium process, excellent corrosion resistance,and significant cost savings. In particular, the issues of brushedcopper, such as burring, can be completely eliminated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention will be best understood by referring to thefollowing detailed description of some illustrative embodiments inconjunction with the accompanying drawings, in which

FIG. 1 is a flow chart of a surface treatment method according to anembodiment of the present invention; and

FIG. 2 is a picture showing the arrangement of the test items.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, a surface treatment method isprovided. The surface treatment method is advantageous for substratesthat are made of plastics or metals. The present invention can beutilized in connection with a variety of applications in a multitude ofdifferent industries, such as bathroom fittings (e.g. showers), consumerelectronics (e.g. mobile phone), automobiles, etc. Consumer electronicshousing components that may be advantageously provided with a highlydecorative surface in accordance with this invention include housingcomponents for cellular telephones. The surface treatment method of thepresent invention provides a decorative metal finish on a metal surfaceof a plastic or metal article, which yields a high quality finish, isless expensive, and is environmentally friendly.

A surface treatment method 100 according to an embodiment of the presentinvention is shown in FIG.1. In step 110, a matte nickel plating layeris formed on a substrate. The substrate is made of acrylonitrilebutadiene styrene (ABS) resin. While the embodiment utilizes a plasticsubstrate, it will be understood that any conductive or non-conductivematerial may be utilized. For example, in addition to the ABS resinsubstrate, other non-conductive substrates such as rubber, ceramic, andwood as well as metal substrates such as copper, nickel, chromium,titanium, or zirconium may alternatively be utilized in accordance withthe present invention. Before the plating of the matte nickel, thesubstrate may undergo several cleaning processes, such as ultrasonic waxremoval, water washing, ultrasonic oil removal, spray washing, etc., andthen roughened to provide sufficient mechanical interlock between thesubstrate and the overlying layer.

The matte nickel plating layer may be deposited on the entire surface ofthe substrate by using the electroless nickel plating, which involvesdipping the substrate in a bath of plating solution, where a reducingagent, like hydrated sodium hypophosphite (NaPO₂H₂.H₂O), reacts with thenickel ions to deposit the nickel layer. The plating solution typicallyhas eight components: nickel, a reducing agent, a complexing agent,stabilizers, buffers, brighteners, surfactants, and accelerators. Nickelsulfate is a typical nickel source, and sodium hypophosphite is atypical reducing agent. The complexing agent is necessary to increasephosphate solubility and to prevent the white-out phenomena by slowingthe reaction. Carboxylic acids or amines are typical complexing agents.Stabilizers, like lead, sulfur, or organic compounds, slow the reductionby co-deposition with the nickel. Most complexing agents act as buffers.Brighteners are mostly co-deposited with nickel, and usually arestabilizers, like cadmium or certain organic compounds. Surfactantslower the surface tension to reduce pitting and staining. Acceleratorssuch as sulfur compounds are added to overcome the slow plating ratecaused by complexing agents and usually are co-deposited, oftendiscoloring the deposit. Preferably, the thickness of the matte nickelplating layer may be greater than 10 μm. Indeed, the thickness of thematte nickel plating layer is preferably in the range of 10 μm to 100μm.

Thereafter, in step 120, the matte nickel plating layer is brushed toform a brushed surface on the substrate such that the substrate has atextured appearance. The brushed finishing may be carried out using anyconventional brushing process, e.g. using a brushing wheel to producestriations on the matte nickel plating layer. Conventionally, thebrushing process is carried out on the copper layer, which often causesburring issue and deteriorated functionality. In the present disclosure,the brushing process is performed on the matte nickel plating layer,which has at least 20% higher yield than the conventional brushedcopper. In addition, the issues of brushed copper, such as burring ordeteriorated functionality, can be completely eliminated in the presentinvention.

Next, in step 130, the brushed surface of the substrate isultrasonically degreased to remove oils from the brushed surface. Theultrasonic degreasing may be carried out in a hot immersing oil removaltank equipped with an ultrasonic generator and a heater and containingan oil removal powder (such as sodium hydroxide) of a concentration of30-80 g/L at a temperature of 40-60° C. for 3-15 minutes. Preferably,the temperature is between 45° C. and 55° C. Ultrasonic high frequencyenergy breaks off oil structure and adhesion thereof to the surface ofthe substrate, and simultaneously the alkaline degreaser may undergosaponification with the oil to obtain an ultrasonically degreasedsurface.

Subsequently, the ultrasonically degreased surface undergoeselectrolytic degreasing to remove workpiece surface grease in step 140before electroplating. The electrolytic degreasing may be carried out ina electrolytic tank equipped with a heater and comprise the followingsteps: injecting an electrolyte into the electrolytic tank, hanging aworkpiece on a fixture, dipping the workpiece into the electrolyte, andelectrifying the electrodes at a temperature of 40-60° C. for 0.5-5minutes. Preferably, the temperature is between 45° C. and 55° C. Theelectrolyte may contain an electrolytic degreasing powder, such assodium hydroxide, of a concentration of 30-80 g/L. By the technicalscheme of the electrolytic degreasing, the electrolyte can morethoroughly degrease the workpiece, is ideal in degreasing effect, andensures the quality of the subsequent plating.

Next, in step 150, the substrate is immersed in an acid solution in anactivation tank for 0.1-2 minutes. The acid solution is comprised ofactivated acid salt and water. The activated acid salt mainly containssodium hydrogen sulfate. Afterwards, the acid-activated surface of thesubstrate may be washed using water, followed by the formation of anon-leveling nickel plating layer in step 160. The plating process ofthe non-leveling nickel (Watts) is well known in the art, and, forexample, it may use the Watts nickel bath composed of nickel sulfate,nickel chloride, and boric acid as the electrolyte solution. Once thesubstrate has been prepared, it is immersed into the electrolytesolution and is used as the cathode. The nickel anode is dissolved intothe electrolyte solution to form nickel ions. The ions travel throughthe solution and deposit on the cathode. In the present embodiment, thenon-leveling nickel plating process is carried out at a voltage of 3.5-5V and a temperature of 45-55° C. for 10 minutes to obtain thenon-leveling nickel plating layer of about 2-5 μm.

Afterwards, in step 170, a bright chromium layer is plated on thenon-leveling nickel plating layer to enhance the salt spray corrosionresistance. The plating process of the bright chromium layer may use ananode made of lead-tin alloy containing 6-8% of tin and an electrolytecomposed of a chromic anhydride with a concentration of 270-290 g/L anda sulfuric acid with a concentration of 0.9-1.2 g/L. Preferably, thechromium plating is carried out at a temperature of 38-42° C. for 4-8minutes. The thickness of the bright chromium layer is preferably in therange of 300 nm to 600 nm.

Next, in step 180, the substrate is load into a vacuum chamber ofmagnetron sputtering equipment to vapor deposit a chromium film byphysical vapor deposition (PVD) on the chromium plating layer. Forexample, a chromium sputtering target of 99% purity can be utilized.Preferably, the chromium is applied to form a uniform layer that isabout 100-200 nm thick and that comprises at least about 99% chromium byweight. The chromium film is utilized to provide the overall coatingwith hardness so that the coating is significantly resistant tocorrosion.

Corrosion Resistance Test

To further illustrate the efficacy of the present invention, 45 testitems of hand shower were prepared according to the surface treatmentmethod of the present invention for corrosion resistance test followingASTM B368 test standard. The corrosion resistance test is conductedthrough the salt spray test method, which uses the CASS test solution ofTable 1 and the process parameters of Table 2. The test items of handshower were arranged as shown in FIG. 2.

TABLE 1 CASS test solution Distilled water 95% (L) 19.0 NaCl 5% (g) 1000CuCl₂•2H₂O (g) 5.7538 Acetic acid (ml) 21 Specific gravity 1.036 PH 3.08

TABLE 2 Process parameters Air pressure (MPa) 0.10 Temp. of saturationtower (° C.) 62.5 Temp. of chamber (° C.) 49.0 Collected solution volume1.5 (ml/hr/80 cm²) Collected solution gravity 1.031 Collected solutionPH 3.24

After the test duration of 40 hours, no visible defect was observed onthe surface of all the test items, which means all the test items passedthe corrosion resistance test following ASTM B368 test standard usingCASS test solution.

It must be pointed out that the embodiments described above are onlysome embodiments of the present invention. All equivalent steps whichemploy the concepts disclosed in this specification and the appendedclaims should fall within the scope of the present invention.

What is claimed is:
 1. A surface treatment method comprising: forming amatte nickel plating layer on a substrate; performing a brushedfinishing to the matte nickel plating layer to form a brushed surface onthe substrate; performing an ultrasonic degreasing to the brushedsurface to form an ultrasonically degreased surface; performing anelectrolytic degreasing to the ultrasonically degreased surface to forman electrolytically degreased surface; performing an acid activation tothe electrolytically degreased surface to form an acid-activatedsurface; forming a non-leveling nickel plating layer on theacid-activated surface; forming a chromium plating layer on thenon-leveling nickel plating layer; and forming a chromium film on thechromium plating layer by physical vapor deposition.
 2. The surfacetreatment method as claimed in claim 1, wherein the substrate is made ofa plastic or a metal.
 3. The surface treatment method according to claim2, wherein the plastic is acrylonitrile butadiene styrene (ABS) resin.4. The surface treatment method according to claim 2, wherein the metalis copper, nickel, chromium, titanium, or zirconium.
 5. The surfacetreatment method according to claim 1, wherein the ultrasonic degreasinguses an oil removal powder.
 6. The surface treatment method according toclaim 5, wherein the oil removal powder contains sodium hydroxide. 7.The surface treatment method according to claim 1, wherein theultrasonic degreasing is performed at a temperature of 45-55° C.
 8. Thesurface treatment method according to claim 1, wherein the electrolyticdegreasing uses an electrolytic degreasing powder.
 9. The surfacetreatment method according to claim 8, wherein the electrolyticdegreasing powder contains sodium hydroxide.
 10. The surface treatmentmethod according to claim 1, wherein the electrolytic degreasing isperformed at a temperature of 45-55° C.
 11. The surface treatment methodaccording to claim 1, wherein the acid activation is performed byimmersing the substrate in an acid solution.
 12. The surface treatmentmethod according to claim 11, wherein the acid solution is comprised ofactivated acid salt and water.
 13. The surface treatment methodaccording to claim 1, wherein the non-leveling nickel plating layer isformed by using the Watts nickel bath.